Okay, before doing this you need to say what series you like and what sort of characters you like. It's fine asking for help, but there are so many things I can suggest to you that you may not necessarily like.

However, I am trying to get a full iDOLM@STER group for Hyper Japan (including, hopefully, a performance). You're welcome to take part if you wish?

It's less who could I cosplay? And more Who do I like enough to cosplay. That's how I started. Generally go with who you like to cosplay as. When you start out it helps to band together with some friends doing the same sort of thing to get a good feel for it.

Failing that just go with something you like. The rest will just happen! Think of any particular games or series where you've liked an outfit or generally liked the character and just go for it!

I remember asking this question a while ago, and people telling me that who I cosplayed was a personal decision, and I'd have to figure it out for myself. And now I see that they were completely right!
The above comments cover this for the most part. It all depends on what genre of gaming / anime / etc. you like, and character personalities you admire. Good luck finding your right character

As others have said, it's completely up to you. For instance I think you'd make a lovely Sailor Jupiter or Venus (depending on how you like your hair/wigs) but you might despite the Sailor Moon series - making what I think rather invalid.

Something else to consider is budget, your normal clothing style (for instance, I'm doing Lady Sif at Expo and it's only now I'm having second thoughts about her rather... revealing 'skirt', and the time you can invest in the costume if you want to make it yourself.

There's lots of brilliant characters out there, some requiring less or more work to build. Maybe if you're having problems deciding, print out images of all your favourite characters, pin them to a board and throw a dart?

Literally couldnt have put it better with what folks are saying on here! your cosplays really pop when its a character you feel something for, for instance Superman and Captain Marvel for me are childhood heroes and I know the characters alot and im told that shows.

failing that I think you would make a really good Supergirl, Pheonix from X-men, Rogue, shadowcat, Mary Marvel from Shazam and Batgirl